200x 83'-85' head flow numbers.

[oscarmayer]

stock HP on these were not as much as you guys think. most were around 9-11HP. today's chinese 200CC motors that are remakes fo the old honda stuff but have higher compression are barley touching the 12-13h mark. so I would get 11 hp would probebly be about right for the 200x in stock form.
getting 18hp out of a 200x is a big deal (we are talking wheel power not flywheel). getting 22hp range means a ton of work and stroking was done usually when proeprly dynoed by a dyno that is set "correctly" not to fudge numbers. Mustang and dyno-dynamic dynos are load bearing and thus provide a much more accurate results. Others are not load bearing and are ususally reading about 12015% higher due to inaccuracy of the dyno by not having a load.

[Mickey Dunlap]

Yes every head is different. I get a lot of Yamaha Warrior customers that want big valves. A long time ago I tried a 900 Kawasaki street bike valve in them because it fit right in. I told this to Kibble White so now they sell them. What I didn't tell them is they killed the flow. When I tell customers this they don't understand that the stock valve flows more because of the back side shape. They want it anyway, so I have to tell them I don't want the job then.

[Dave8338]

I see these numbers and have always wondered why, so few details about the specific hp and torque numbers, are available.

Take a look at the spec sheet for a 1983 XL200R Enduro bike. Same basic design principle, engine parts, etc.

Max Power
18 hp @ 8000 rpm

Max Torque
1.7 kgf-m @ 6500 rpm
http://www.motorcyclespecs.co.za/mod...l200r%2083.htm

Which set of numbers are wrong. Where the above stats using HP at the crank?

[xrider]

The last time I had my 200x on the dyno it put down 27 hp at the wheels. Thats with extensive head work, a +6mm long rod stroker and 12:1 compression.

[Dave8338]

The last time I had my 200x on the dyno it put down 27 hp at the wheels. Thats with extensive head work, a +6mm long rod stroker and 12:1 compression.

I would believe that. I am MUCH more familiar with motorcycles and how to get power out of them. A 200cc engine only making 11-12HP and extrapolate that out to a four cylinder 800cc bike and you would have a 48HP inline four ? ? ? Yes... I know the math doesn't work that linear, just making an example.

[Mickey Dunlap]

I see these numbers and have always wondered why, so few details about the specific hp and torque numbers, are available.

Take a look at the spec sheet for a 1983 XL200R Enduro bike. Same basic design principle, engine parts, etc.

Max Power
18 hp @ 8000 rpm

Max Torque
1.7 kgf-m @ 6500 rpm
http://www.motorcyclespecs.co.za/mod...l200r%2083.htm

Which set of numbers are wrong. Where the above stats using HP at the crank?

I would say those are crank numbers.

[Mickey Dunlap]

The last time I had my 200x on the dyno it put down 27 hp at the wheels. Thats with extensive head work, a +6mm long rod stroker and 12:1 compression.

Those are very high numbers, that's why I wanted to take yours and mine to the dyno I use. Now I'm just going to take mine with a good head on it because I know where it was and that will give me a idea how these Dyna Jets work compared to the Powroll dyno.

[Dave8338]

I think you're correct, Mickey. Be interesting to have a cam out of one of those, to run numbers on. Same as the ATC ?

If it is at the crank, and others have stated that 11 RWHP is what is to be expected, that means that there is a ~ 40% loss in the drive train. This I do not believe.
Any average that I've calculated and observed on several projects from 2 to 4 wheels, puts the RWHP losses in the 15% range.

The bore and stroke numbers, match what I have going, the XL compression is lower at 9.2 :1 and the XL carb is a 24mm Keihin.

[xrider]

Those are very high numbers, that's why I wanted to take yours and mine to the dyno I use. Now I'm just going to take mine with a good head on it because I know where it was and that will give me a idea how these Dyna Jets work compared to the Powroll dyno.

That should make for a good comparison to the powroll numbers. Mine was on a Dyno jet as well. Curious to see what kind of numbers you pull if you put together a big bore / stroker combo. I am still bound determined to break the 30 HP mark.

[xrider]

Mickey, How much of the 253cc will be stroke and how much will be bore? I'm assuming 6mm on the crank?

[ironchop]

while I was already aware of the fact I had very little understanding of flow when I began cleaning up some casting flaws in my intake track and incorrectly referring to it as "mild porting", I must now humbly admit that I didn`t know just how friggin ignorant I was to what is involved after reading this thread. I did study camshaft theory (a little) and had several calls in to the Megacycle rep before I bought that cam but I think it`s time I STFU and learn more before I attempt this again.

I deserve to feel stupid for not asking more questions of more experts and now all I want to do is tear down my X motor with four hours on it and just send it off and quit pretending I`m doing any good at home on a workbench with my grade-school understanding of flow.

Thanks for sharing the info, Mr. Dunlap

[Mickey Dunlap]

Mickey, How much of the 253cc will be stroke and how much will be bore? I'm assuming 6mm on the crank?

I'm going to go a 8mm stroke with a safe 70mm bore, I could go 7mm but it makes everything right on the edge then. I'm keeping the stock rod with a super lite piston two ring style because we will be 4mm's shorter decks.

[Mickey Dunlap]

while I was already aware of the fact I had very little understanding of flow when I began cleaning up some casting flaws in my intake track and incorrectly referring to it as "mild porting", I must now humbly admit that I didn`t know just how friggin ignorant I was to what is involved after reading this thread. I did study camshaft theory (a little) and had several calls in to the Megacycle rep before I bought that cam but I think it`s time I STFU and learn more before I attempt this again.

I deserve to feel stupid for not asking more questions of more experts and now all I want to do is tear down my X motor with four hours on it and just send it off and quit pretending I`m doing any good at home on a workbench with my grade-school understanding of flow.

Thanks for sharing the info, Mr. Dunlap

It's not about being stupid, I just happen to work at Powroll and was told what to do and where to grind and where not to, but you still have to do a lot of R&D on each head. I'm just now after working on my v-twin Kawasaki's for 17 years to the point where my heads make a lot of power, more then I thought I would ever see. So it just takes time, and it's not all just about flow numbers. The 2 valve motors need all the help they can get and I still have more work to do. The only way I'm going to get any high HP numbers out of the 253 is a very big cam.

[ironchop]

two questions

I`ve had some conflicting answers from local builders about "polishing"

some builders told me NOT to make the intake runner glass smooth but maybe a tiny bit rough because of something called "fuel shear?" but that I should polish the exhaust runner as smooth as I can get it. Now I don`t know enough to say wether this applied to a two-valve motor motor or not as he builds and races newer machines with more valves. What are your experiences and did I misunderstand what they were telling me?

We used to back-cut the radius between the valve and stem on our bracket drag cars for more flow but it wasn`t a lathe cut on the valve on backside of the seat area but rather I grinded them in a spin fixture on a precision grinder making the radius between the stem and the big part (name escapes me) smaller. This is NOT what you meant by a 30 degree back-cut, right?

I like your website, BTW.

[xrider]

I'm going to go a 8mm stroke with a safe 70mm bore, I could go 7mm but it makes everything right on the edge then. I'm keeping the stock rod with a super lite piston two ring style because we will be 4mm's shorter decks.

Very nice. If you get it done and get rwhp numbers over 30. I'll get a motor headed your way.